1. Field of the Invention
This invention pertains to a method and an apparatus for reforming electrically responsive articles and more particularly to a method and apparatus for electromagnetically reforming at least a portion of the sidewalls of generally cylindrically shaped containers.
2. Description of the Art
Various methods are known in the art for shaping articles such as metallic containers. U.S. Pat. No. 1,711,445, for example, discloses a method in which a plunger and compressed air cooperate to bulge container sidewalls against the face of an adjacent die. U.S. Pat. No. 2,787,973 pertains to a method for hydraulically expanding a container into tight contact with a surrounding mold. High voltage discharge forming of containers against a fixed mold is described, for example, in U.S. Pat. No. 3,654,788. These and other methods result in reforming the sidewalls of thin walled containers to conform to a mold configuration against which the sidewalls are directed.
Another working method known in the art is called magnetic forming or electromagnetic forming. Such a method involves forming materials with the use of magnetic fields of relatively high intensity. In electromagnetic forming an electrical current is passed through a coil consisting of a conductive wire which is typically supported by a nonconductive structure. The current produces a pulsed magnetic field which induces a current in an adjacent conductive workpiece. The induced current in the workpiece reacts with the magnetic field to produce a force which is directed against the adjacent workpiece. An exemplary electromagnetic forming coil is described in U.S. Pat. Nos. 3,383,890 and 3,599,461.
Electromagnetic forming has been employed in a number of various applications. For example, U.S. Pat. No. 3,540,250 discloses the use of a magnetomotive coil used to constrict large diameter metal tubes, and U.S. Pat. No. 4,285,224 pertains to the use of an electric pulse to expand tubes such as those employed in heat exchangers. Other applications for electromagnetic forming include reinforcing lock seams by expanding metallic locking bands.
A method of magnetomotive forming of cylindrical objects such as cans is disclosed in U.S. Pat. No. 3,810,373. This method involves subjecting the object to a very high outwardly directed force wherein the object is compressed against a surrounding die. An exemplary die, described in U.S. Pat. No. 3,810,372, is for forming selected impressions in the cylindrical object.
Despite prior work in the electromagnetic area, there is still a need for further improvement to provide a method and an apparatus for electromagnetically reforming container bodies which are not cumbersome, not excessively expensive and do not tend to unduly restrict the demand for high production rates.